The invention relates to mufflers for noise-silencing.
The invention arose during continuing development efforts directed toward mufflers such as shown in U.S. Pat. Nos. 6,076,632, 6,250,422, 6,457,553, all incorporated herein by reference. The invention also arose during continuing development efforts directed toward cost reduction.
Mufflers for internal combustion engines, particularly small engines, e.g. for lawnmowers, tractors, and the like, are typically made with two shells or stampings that together comprise the outer shell of the muffler. The shells are joined together in a crimping operation. This process has been reliable and efficient, resulting in a low cost muffler. One problem which may be encountered is that many small engines exhibit an afterfire condition upon engine shutdown. This happens when unburned fuel is ignited by hot internal muffler surfaces causing an explosion in the muffler. This afterfire explosive force in the muffler can rupture the muffler at the seam of the two shells. Countermeasures for afterfire survival typically include making the muffler shells thicker or adding tack welds to the seam joint to keep the joint from separating during an afterfire. Both of these solutions may add objectionable cost.
The present invention provides a simple and effective solution to the noted afterfire problem, in a cost-effective manner.